Free Flip-Book Zoology Class 11th & 12th by Study Innovations

Anterior surface of the head of an insect c

Source: http://www.thinkquest.org

Parts of an Arthropod leg

Source: http://www.thinkquest.org

Chapter 3 49

Classification :
Subphylum Trilobita
(1) Most primitive, extinct, marine arthropods of Cambrian to Permian
rocks. Body covered by a hard segmented shell; They have a distinct
head of four fused somites with a pair of antennae, four pairs of
appendages and a pair of eyes.
(2) Trunk is divided into 3 lobes by two longitudinal furrows.
(3) Each segment, except the last one, bears a pair of biramous jointed
appendages.
Example – Triarthrus.
Subphylum Chelicerata
(1)They are mostly terrestrial, free living and small sized.
(2) Body distinguished into head, thorax and abdomen (= opisthosoma).
Head and thorax are fused to form a cephalothorax or prosoma.
(3) Cephalothorax bears eyes and six pairs of appendages – One pair of
clawed and jointed chelicerae in place of mandibles, one pair of
pedipalps, and four pairs of walking legs. Antennae absent. Abdomen
may or may not have appendages, but is distinguished into a large and
broader mesosoma, a small metasoma and a long and narrow, tail–like
telson.
(4) Respiration by gills, book lungs or tracheae.

c(5) Excretion by malpighian tubules or coxal glands, or both.

(5) Sexes mostly separate; females oviparous; development direct or
through a larval stage.
This subphylum is divided into three classes-
Class (1) – Merostoma
(1) They are Marine.
(2) Respiration by gills.
(3) Cephalothroax with lateral compound eyes and six pairs of
appendages.
(4) Abdomen with 5 to 6 pairs of gill bearing appendages.
(5) Hind end forms a long like telson.
Example– Limulus (The king-crab). Limulus is a living fossil.

Chapter 3 50

Class (2) – Arachnida
(1) Mostly terrestrial.
(2) Respiration by book lungs or tracheae.
(3) Abdomen without appendages.
(4)Some have poison glands and poison fangs, jaws of stings.
(5) Gills absent.
(6) Life cyle without metamorphosis.
Examples – spiders, scorpions, mites, ticks, Palamnaeus (scorpion),
Lycosa (the common web–spinning spider; web–spinning glands are
located in posterior part of abdomen)
Class (3) – Pycnogonida or Pentapoda
(1) Small marine sea spiders.
(2) Cephalothorax is 3 segmented; forms major part of body; abdomen
vestigial.
(3) Suctorial mouth on top of a long proboscis.
(4) No special respiratory and excretory organs.
(5) Unisexual; females oviparous. Eggs carried by males.
Example – Nymphon.
Subphylum Mandibulata or Antennata
(1) Body divided into head and trunk, or head, thorax and abdomen.
(2) 1 or 2 pairs of antennae, 1 pair of mandibles in place of chelicerae,

cone or more pairs of maxillae and 3 or more pairs of walking legs.

(3) Respiration by gills or tracheae.
(4) Excretion by malpighian tubules or antennal glands.
(5) Unisexual
It is divided into six classes
Class (1) – Crustacea
(1) Mostly aquatic.
(2) Body divided into cephalothroax and abdomen.
(3) On dorsal side, cephalothorax covered by a thick exoskeletal called
carapace.
(4) Respiration through body surface or by gills.
(5) Excretion by special coxal glands in antennae or maxillae.

Chapter 3 51

Examples –Palaemon (prawn), Cancer(Crab) , Cyclops (Water-flea),
Crayfish.
Class (2) – Insecta
(1) Aquatic, terrestrial or aerial.
(2) Body divided into head, thorax and abdomen.
(3) Segments 3 in thorax and 10 in abdomen.
(4) Legs typically 3 pairs (Hexapoda); The aerial forms have one or two
pairs of wings.
(5) Head with 1 pair of large, compound eyes, 1 pair of antennae and
variously modified mouth–parts.
(6) Respiration by tracheal sysem.
(7) Excretion by specialized malpighian tubules.
(8) Unisexual; females oviparous.
Examples – Periplaneta (Cockroach), Musca (house-fly), Mosquitoes,
locusts butterflies, bees, wasps, termites, silverfish (Lepisma), beetles,

cetc. Silverfish is not a fish.
Parts of an insect body

Source: http://www.thinkquest.org

Class (3) – Diplopoda (Millipedes)
(1) Terrestrial, long body, cylindrical, worm like.
(2) Head with 1 pair each of antennae, mandibles and maxillae; 2 pairs

Chapter 3 52

of simple eyes.
(3) Thorax of has 4 segments, each except the first bears a pair of
jointed legs.
(4) Abdomen with each segment apparently formed by fusion of two
and, hence, bears 2 pairs of legs.
(5) Respiration by tracheae.
(6) Excretion by malpighian tubules.
(7) Unisexual; gonad single; females oviparous.
Example – Julus (millipede)

Class (4) – Chilopods (Centipedes)
(1) Terrestrial with long, worm like body divided into head and trunk.
(2) Boy segments not fused in pairs; each segment with a single pair of
legs; first pair of legs is claw like and contains a poison gland.
(4) Respiration by tracheae.
(5) Unisexual; females oviparous or viviparous.
(6) Excretion by malpighian tubules.
Example – Scolopendra (centipede).

cPractice Test Paper

1.Cestodes are distinguished from other flatworms by the absence of
(a) Nervous System (b) Digestive system (c) Excretory system (d)
Reproductive system

2.Playhelminthes represents an example of
(a) Cellular grade of organisation (b) Tissue grade of organisation (c)
Organ-system grade of organisation (d) Tissue-organ grade of
organisation

3.The excretory organs of flatworms are

Chapter 3 53

(a) Flame cells (b) Nephridia (c) Malpighian tubules (d) Rennate glands

4.Body cavity of Ascaris is
(a) Pseudocoel (b) Enterocoel (c) Coelom (d) Acoelom

5.Metamerically segmented body is present in
(a) Earthworm (b) Leech (c) Nereis (d) All of the above

6.Earhworm is placed in the group

(a) Oligochaeta (b) Polychaeta (c) Hirudinea (d) Crustacea

7.Peripatus is a connecting link between
(a) Reptiles and birds (b) Annelida and arthropoda (c) Mollusca and
annelida (d) Mollusca and arthropoda

8.The connecting link between annelida and mollusca is
(a) Neopilina (b) Nautilus (c) Glochidium larva (d) Valiger larva

'9.Hexapoda' is another name of
(a) Crustacea (b) Arachnida (c) Insecta (d) Archiannelida

10.In cockroach, the excretory organs are

c(a) Malpighian tubules (b) Nephridia (c) Malpighian corpuscles (d)

Solenocytes (flame cells)

11.The Nematodes have simple excretory system in the form of a ……

12.The excretory organs in platyhelminthes include special cell known
as……..

13. The true coelom in the animal kingdom appears first time in the
phylum…..

Chapter 3 54

14. The locomotion in Annelids takes place by unjointed chitinous
appendages called as …..

15. What is clitellum
16.Enlist respiratory organs found in Arthropods
17. Mention atleast three excretory organs found in Arthropoda
18. Write down the parts of an arthropod leg in a sequence

19. Write down the respiratory and excretory organs in insects

20. What is pseudocoel? c
Answers and solutions

1. b
2. c
3. a
4. a
5. d
6. a

7. b

8. a

9. c

10. a

11. Rennete cell

12. Flame cells

Chapter 3 55

13. Annelida

14. Setae

15. The clitellum is a glandular tissue which secrets cocoon
during development

16. gills, book gills, tracheae and book lungs
17. green glands, coxal glands and malpighian tubules

18. Coxa, basidium, Ischium, merus, carpus, propodus, and
dactylus

19. Respiration by tracheal sysem and excretion by specialized
malpighian tubules

20. The most important characteristics of phylum nematoda is
that the space between body wall and alimentary canal is not
lined by peritonium / mesoderm. Such a body cavity is known as
a false body cavity, or pseudocoel. The pseudocoel represents

cthe persistant embryonic blastocoel

Chapter 3 56

Animal Kingdom Part 4
(Phylum Mollusca, Echinodermata and Hemichordata)

Phylum Mollusca
The mollusks are soft bodied animals. (L., mollis or molluscum =
soft)The body is unsegmented and enclosed within a skin fold
(mantle/pallium). The mantle secretes a calcareous shell. They have
about 80,000 living and 35,000 extinct species known. Aquatic or
terrestrial. Malacology or Conchology is the study of molluscs and their
shells.
Body Plan of molluscs:-
•head: contains sensory organs
•foot: Muscular organ used for locomotion
•visceral mass: contains digestive, reproductive, circulatory organs
•mantle: skin of the dorsal body wall. It secretes the shell (if there is

cone). The mantle cavity contains gills or lungs
Source:http://infusion.allconet.org/webquest/PhylumMollusca.html

General characters:
(1) The molluscs have bilateral symmetry, but snails are asymmetrical
(2) They are triploblastic, coelomate animals. True coelom is reduced

Chapter 4 57

and limited to kidney and gonads. The haemocoel is well developed.
(3) They have organ system grade of organization.
(4) The molluscs are provided with one or two calcareous shells. The
shells may be external or internal.
(5) Respiration is carried out by the gills or pulmonary chambers.
(6) The digestive system is well developed with a characteristics rasping
organ called a radula and a hepatopancreas.
(7) The circulatory system is of open type except in cephalopods.
(8) The excretion by organ of Bojanus or Kebers organ(pericardial
gland).
(8) The nervous system is well developed.
(9) The sensory organs are eyes, statocysts and osphradia. The
osphradia are for tasting chemical nature of water
(10) Sexes are separate, or hermaphrodites.
(11) The development either direct or indirect involving veliger and
trochophore larvae

Classification:
Class 1. Aplacophora
(1) The head, mantle, foot, shell and nephridia are absent.
(2) The body is covered with cuticle.

c(3) The digestive tract is straight with radula.

(4) A mid dorsal longitudinal keel or crest present .
Example : Chaetoderma

Class 2. Monoplacophora
(1) The shell is composed of a single valve.
(2) The head is without eyes and tentacles.
Example : Neopilina galatheae
Neopilina is a living fossil and connecting link between Annelida and
Mollusca.

Class 3. Polyplacophora

Chapter 4 58

(1) The shell is composed of a longitudinal series of 8 shell plates.
(3) The foot is flat and ventral.
(4) The radula is well developed.
Example : Chiton

Chiton

Source: http://www.thinkquest.org

Class 4. Gastropoda
(1) These animals appear to be moving on their stomach. Hence the
name gastropoda.
(2) Gastropods are asymmetrical.
(3) The shell is univalve and spirally coiled.
(4) The head is distinct with tentacles, eyes and a mouth.
(5) The foot is ventral and muscular.

c(6) The buccal cavity is provided with a radula.

(8) The circulatory system is open.
(9) The sexes are mostly separate.
(10) The development includes veliger and trochophore larvae.
Examples : Haliotis, Cyprea (Cowrie) Pila (apple snail), Murex (rock
shell) Aplysia (sea hare), Doris (Sea Lemon)

Class 5. Scaphopoda
(1) They have a tubular shell opening at both ends.
(2)The foot is boat shaped
Examples : Dentalium

Chapter 4 59

Dentalium is commonly called tusk shells.

A scaphopod, or tooth shell, burried in the sand

Source: http://www.thinkquest.org

Class 6. Pelecypoda
(1) They are bilaterally symmetrical and laterally compressed.
(2) The shell is composed of two distinctive shell plates.
(4) No distinct head.
(5) The sexes are separate or united.
(6) The development is indirect having a glochidium larva.

cExample : Mytilus, Unio, Tredo.

Pearl oyster belongs to the class pelecypoda.

Class 7. Cephalopoda
(1) The foot is modified into arms and siphon (funnel).
(2) The shell may be either absent or rudimentary; it may be internal or
external.
(3) The odonotophore with a radula is present.
(4) The ink glands for offence and defence are present.
(7) The sexes are separate.
(8) The development is direct hence no metamorphosis and larval

Chapter 4 60

stage.
Example : Nautilus, Loligo Sepia, Octopus

Dorsal view of a squid (loligo) in swimming position

Source: http://www.thinkquest.org

Phylum Echinodermata

The term “Echinodermata” means spiny skin (Gr., echinos = spiny +
dermatos = skin). They have a tough, leathery, spiny skin and a
mesodermal endoskeleton made up of calcareous plates or ossicles.
The echinoderms belong to deuterostome line of evolution. Their larva
have the basic bilateral symmetry but the adults have pentamerous
radial symmetry. About 6,000 living species are known.

cGeneral characters:

(1) Echinoderms are exclusively marine, free living, triplobalstic and
coelomate animals.
(3) They are radially symmetrical. The radial symmetry is a secondary
character in the adult echinoderms.
(4) They have organ system level of body organization.
(5) They have a characteristics water vascular system with tube feet for
locomotion, feeding and respiration.

Chapter 4 61

(6) Circulatory system is of the open type.
(7) The sensory organs are poorly developed.
(8) The excretory organs are absent.
(9) They have pincer like structures on the body surface in between the
spines called pedicellariae. The pedicillariae are used for cleaning the
surface off debris.
(10) Development is indirect with bilaterally symmetrical larva.
(11) Respiration by dermal branchiae or papulae in star fishes,
peristomial gills in sea urchins, genital bursae in brittle stars, and
cloacal respiratory tree in holothurians

c(12)They have great power of regeneration.

Chapter 4 62

General Anatomy of an Echinoderm (Starfish)

Source: http://www.thinkquest.org

Classification:
Class 1. Asteroidea
(1) It includes starfishes or sea stars.
(2) Arms five and not sharply demarked from the central disc.
(3) Tube feet with suckers in orally placed ambulacral grooves.

c(4) Anus and madreporite aboral.

(5) Pedicellariae present.
(6) Slow-creeping, predaceous and scavangerous.
Examples : Astropecten, Oreaster (= Pentaceros), Asterias.
Class 2. Ophiuroidea
(1) It includes Brittle-stars.
(2) Body star-like with arms sharply demarked off from the central disc.
(3) Pedicellariae absent.
(4) Stomach sac-like without anus.
(5) Ambulacral grooves absent or covered by ossicles; tube feet without
suckers.

Chapter 4 63

(6) Madreporite oral.
Examples : Ophiura, Ophiothrix, Ophioderma.

Oral view of the disk of a brittle star

Source: http://www.thinkquest.org

Class 3. Echinoidea :
(1) The body is not divided into arms and is globular (sea urchins), or
flattened disc-like (sea-cakes).
(2) Mouth present at lower end, covered by five strong, sharp teeth,
forming a biting and chewing apparatus called “Aristotle's Lantern”.
(3) Tube feet with suckers.
(4) Skin ossicles are fused together to form a rigid globular, disc like, or
heart-shaped shell or test with movable spines.
(5) Pedicellariae present.

c(6) Anuspresent.

(7) Larval forms Pluteus and Echinopluteus.
Examples – Sea urchins and sand dollars.

Chapter 4 64

Oral view of the Atlantic sea urchin

Source: http://www.thinkquest.org

Class 4. Holothuroidea
(1) Body long, cylindrical like a cucumber; elongated in oral aboral axis;
without arms.
(2) Mouth at anterior and anus at posterior ends.
(3) Mouth is surrounded by many hollow retractile tentacles.
(4) Tube feet usually present; sucker-like.
(5) Skin leathery but without spines or pedicellariae.

c(6) Respiration and excretion by two long, highly branched tubes

(known as respiratory tree) in cloaca.
(7) Larval form Auricularia.
Examples – Holothuria, Cucumaria.

Chapter 4 65

Sea cucumber (cucmaria frondosa)

Source: http://www.thinkquest.org

Class 5. Crinoidea
(1) Body pentamerous; distinguished into a small, circular central disc
and five or more (in multiples of five) long, branched arms radiating
from the disc.
(2) Disc enclosed in a cup shaped calyx of calcareous plates; calyx
attached to a substratum with the help of a stalk or simply by its aboral

csurface.

(3) Mouth and anus both on oral surface.
(4) Tube feet sucker like; restricted to central disc.
(5) Some forms (sea lilies) permanently sessile and attached to sea
bottom by a stalk; others (feather stars) free-swimming.
(6) Pedicellariae absent in skin.
Examples – Sea lilies and Feather stars (Antedon)

Chapter 4 66

A stalked feather star

Source: http://www.thinkquest.org

Phylum Hemichordata :
(Gr. hemi, half; chorde, cord)
The hemichordates were earlier considered as a subphylum of
Chordata but now it is undoubtedly placed as a phylum under non
chordates.
General Characters:
(1) Body divided into 3 regions: Proboscis, collar and trunk.
(2)The so called notochord in hemichordates is not a true notochord

cbut it is a hollow outgrowth from the roof of buccal cavity. Therefore, it

is also called as Buccal diverticulum or stomochord. Stomochord is
confined to proboscis and non homologous with that of chordates.
(3) Gill slits present but dorsal in position
(4) Ventral nerve chord
(5) Respiration by gills
(6) Circulatory system open
(7) Development mostly indirect with a free swimming larva called
Tornaria larva

Chapter 4 67

Fig Balanoglossus (above)

CLASSIFICATIPON:

Class 1. Enteropneusta : (Gr. enteron, gut; pneustos, breathed). Body
large and worm-like. Gill slits numerous. Intstine straight. Acorn or

ctogue worms. 70 species. Balanoglossus, Saccoglossus.

Class 2. Pterobranchia : (Gr. pteron, feather; branchion, gill). Body small
and compact. Gill-slits one pair or none. Intstine U–shaped.
Pterobranchs. 20 species. Cephalodiscus, Rhabdopleura.

Practice test Paper
1.Natural pearl is a
(a) A molluscan secretion (b) Annelida secretion (c) An arthopoda
secretion (d) An echinodermata secretion

2. Mantle, foot and shell are the character of

Chapter 4 68

(a) Nautilus (b) Echinus (c) Limulus (d) Euplectella

3. Shell of mollusc is produced by its
(a) Radula (b) Thorax (c) Mantle (d) Abdomen

4.Sea hare' is
(a) Aplysia (b) Pila (c) Teredo (d) Septa

5. Main function of pedicellariae in Asterias is
(a) Digestion (b) Excretion (c) Respiration (d) Capture of prey and
removal of debris

6.Aristotle's lantern is a characteristic of the following class of
echinodermata
(a) Echinoidea (b) Ophiuroidea (c) Holothuroidea (d) Asteroidea

7.Antedon belongs to the class
(a) Crinoidea (b) Asteroidea (c) Ophiuroidea (d) Echinoidea

8.Notochord is restricted to the anterior part of body proboscis in
animals of which group
(a) Hemichordata (b) Urochordata (c) Cephalochordata (d) Chordata

9.Presence of a skeleton of calcareous structure is found in all the

cmembers of which phylum

(a) Porifera (b) Echinodermata (c) Mollusca (d) Protozoa

10.The term not applicable to echinodermata
(a) Madreporite (b) Podia (c) Marine (d) Bilateral symmetry

11. The organ used for tasting chemical nature of water…….

12. A living fossil and connecting link between Annelida and Mollusca is
………

13. The glochidium larva is found in the phylum

Chapter 4 69

14. Ink glands found in mollusca are the characteristic of the class……

15. The only non-chordate phylum having mesodermal endoskeleton
made up of calcareous plates or ossicles is……….

16. The free swimming characteristic larva of hemichordates is called
as ……
17. The bipinnaria larva belongs to the phylum…….

18. What are pedicillariae? c
19. What is Aristotle’s Lantern
20. Briefly explain about stomochord of hemichordates

Answers and Solutions
1. a
2. a
3. c
4. a

5. d

6. a

7. a

8. a

9. c

10. d. Echinoderms are radially symmetrical

Chapter 4 70

11. Osphradium

12. Neopilina

13. Mollusca

14. Cephalopods

15. Echinoderms

16. Tornaria

17. Echinodermata

18. The pincer like structures on the body surface in between
the spines in echinoderms are called pedicellariae. The
pedicillariae are used for cleaning the surface off debris.

19. The mouth in class echinoidea is covered by five strong,
sharp teeth, forming a biting and chewing apparatus called
“Aristotle's Lantern”.

20. The so called notochord in hemichordates is not a true
notochord but it is a hollow outgrowth from the roof of buccal
cavity. Therefore, it is also called as Buccal diverticulum or
stomochord. Stomochord is confined to proboscis and non

chomologouswith that of chordates

Chapter 4 71

Animal Kingdom Part 5
(Chordates - General account, Pisces and Amphibians)
The phylum chordata has three most important characteristics:
(1) They have a notochord either throughout life or during early embryonic
development
(2) Dorsal hollow nerve chord
(3) Paired gill slits on either sides of pharynx at some stage; may or may not be
functional

Body plan of Chordates

Source:http://staff.tuhsd.k12.az.us/gfoster/standard/chordate.gif

Other important characters are as follows-
1. Bilaterally symmetrical and metamerically segmented, triploblastic,
coelomate animals having a true coelom, enterocoelic or schizocoelic in origin.
2. A post anal tail usually projects beyond the anus at some stage and may or

cmay not persist in the adult.

3. A cartilaginous or bony, living and jointed endoskeleton present in majority
of members (vertebrates).
4. Pharyngeal gill slits present at some stage; may or may not be functional.
5. Digestive system complete with digestive glands.
6. Blood vascular system closed. Heart ventral with dorsal and ventral blood
vessels. Hepatic portal system well developed.
(7) Excretory system consists of proto-or meso- or meta-nephric kidneys.
8. Sexes separate with rare exceptions.
Outline Classification of Phylum Chordata

Chapter 5 72

Group A. Acrania (Protochordata) cGroup B. Craniata (Euchordata) or
or Lower Chordata
Exclusively marine, small-sized Higher Chordata
chordates Aquatic or terrestrial, mostly large
No appendages, cephalization and sized vertebrates
exoskeleton Usually two pairs of appendages,
well-developed head and
Coelom enterocoelic, formed by exoskeleton present
fusion of pouches budded off from Coelom schizocoelic, formed by
embryonic archenteron. splitting up of mesoderm
Notochord may persist throughout
life and is not replaced by vertebral Notochord replaced by a vertebral
column. No skull, cranium and column. Skull and cranium present
verterbral column
Phyrynx with permanent gill clefts. Phraryngeal gill clefts persist or
disappear
Endostyle present Endostyle absent
Heart chamber less when present. Heart made of 2, 3 or 4 chambers.
No. red blood corpuscles in blood Blood has R.B.Cs
Kidneys protonephridia Kidneys meso– or metanephric
Sexes separate or united. Sexes separate.
Reproduction asexual as well as Only sexual reproduction,
sexual.
Gonoducts usually absent Gonoducts always present

DCihvaispitoenr 5I. Agnatha 73 Division II. Gnathostomata
Without true jaws True jaws present

Paired appendages absent Appendages paired (pectoral &

pelvic) present

Inner ear with 2 semi-circular canals. Inner ear with 3 semi-circular canals

Notochord persistent in adults Notochord persists or replaced by

vertebrae

Classification of chordata :
Phylum chordata can be divided into two groups: Acrania (Protochordata) and
Craniata (Euchordata).
Group A. Acrania (Protochordata) : (Gr. a, absent; kranion, head, or, Gr. protos,
first; chorde, cord). All marine, small, Primitive or lower chordates. Lacking a
head, a skull or cranium, a vertebral column, jaws and brain. About 2,000
species known. The Acrania is divided into three subphyla: Hemichordata,
Urochordata and Cephalochordata
Subphylum I. Hemichordata : (Gr. hemi, half; chorde, cord). Body divided into 3
regions: Proboscis, collar and trunk. Hemichordates are now studied as a
separate invertebrate phylum

Class 1. Enteropneusta : (Gr. enteron, gut; pneustos, breathed). Body large and
worm-like. Gill slits numerous. Intstine straight. Acorn or togue worms. 70
species. Balanoglossus, Saccoglossus.
Class 2. Pterobranchia : (Gr. pteron, feather; branchion, gill). Body small and
compact. Gill-slits one pair or none. Intstine U–shaped. Pterobranchs. 20

cspecies. Cephalodiscus, Rhabdopleura.

Subphylum II. Urochordata or Tunicata : (Gr. oura, a tail; L. chorda, cord).
Notochord and nerve cord only in tadpole-like larva. Adult sac-like, often sessile
and encased in a protective tunic.

CCsqlhauasipsrtt1es..r AA5bscoiudta1ce,2a0:0Ssepsescilieestu. Hniecradt7me4sa.nGiail,l-Mcloelfgtsulnau. mHeerordums.aengi.aAsshcoidwiasns or sea

retrogressive metamorphosis.
Class 2. Thaliacea : Free-swimming or pelagic tunicates. Sometimes colonial.
Salps or chain tunicates. 30 species. Salpa, Doliolum, Pyrosoma.

Subphylum III. Cephalochordata : (Gr. kephale, head; L. chorda, cord).
Notochord and nerve cord present throughout life along entire length of body.
Class Leptocardii : Body fish-like, segmented with myotomes and numerous
gill-slits. Free swimming and burrowing. Lancelets. About 30 species.
Branchiostoma (= Amphioxus), Asymmetron.

Group B. Craniata (Euchordata): They are higher chordates or vertebrates with
distinct head, a vertebral column, jaws and brain protected by a skull or
cranium. The Craniata includes a single subphylum, the vertebrata.

Subphylum IV. Vertebrata : (L. vertebratus, backbone). Notochord
supplemented or replaced by a vertebral column or backbone formed of

coverlapping vertebrae. Usually dioecious. Vertebrates are largest chordate

subphylum including about 46,500 species. The vertebrata is divided into two
divisions: Agnatha and Gnathostomata as follows;

Division I. Agnatha : (Gr. a, not; gnathos, jaw). Jaw less primitive fish-like
vertebrates without true jaws and paired limbs.
Class 1. Ostracodermi. (Gr. ostrakon, shell; derma, skin). It includes extinct
orders of ancient primitive heavily armoured, Palaeozoic, world's first
vertebrates, collectively called the ostracoderms. Caphalaspis, Drepanaspis.
Class 2. Cyclostomata. (Gr. cyklos, circular; stoma, mouth). Body eel-shaped,
without scales, jaws and lateral fins. Mouth rounded and suctorial. Gills 5–16
pairs. Parasites and scavengers. 45 species. Lampreys (Petromyzon) and
hagfishes (Myxine).

Chapter 5 75
Division II. Gnathostomata : (Gr. gnathos, jaw; stoma, mouth). Jawed

vertebrates with true jaws and paired limbs. Gnathostomata is divided into two
super classes. All fishes like aquatic gnathostomes are placed in the superclass
Pisces, whereas all the four legged terrestrial gnathostomes in the superclass
Tetrapoda.

Superclass 1. Pisces Superclass 2. Tetrapoda

Exclusively aquatic Aquatic or terrestrial.

Paired limbs, if present, as fins. Paired pentadactyle limbs present

Median fins present Median fins absent

Skin usually moist and scaly Skin usually dry and cornified

Respiration aquatic, by gills Respiration aerial, by lungs
cExamples : Labeo (rohu), Protopterus (lungfish), Hippocampus (sea horse)
Sense organs functional in water Sense organs functional in air.

It includes fishes only. It includes the classes- Amphibia,

Reptilia, Aves and Mammals

Superclass Pisces

Class 1 Placodermi (Extinct)

• Primitive earliest jawed fishes of Palaeozoic era.

Examples : Placoderms. Climatius, Dinichthys.

Class 2 Chondrichthyes

• Mostly marine with Cartilaginous endoskeleton.

Examples : Scoliodon (dogfish), Chimaera (ratfish).

Class 3 Osteichthyes

• Freshwater as well as marine with bony endoskeleton.

Chondrichthyes (Cartilaginous Fishes/Elasmobranchs

Chapter 5 76

General characters-
(1) Mostly marine and predaceous.
(2) Body spindle shaped.
(3) Fins both median and paired, all supported by fin rays. Pelvic fins
bear claspers in male. Tail heterocercal.
(4) Skin tough with minute placoid scales and mucous glands.
(5) Endoskeleton entirely cartilaginous, without true bones (Gr.
chondros, cartilage + ichthys, fish). Notochord persistent. Vertebrae
complete and separate. Pectoral and pelvic girdles present.
(6) Mouth ventral. Jaws present. Teeth are modified placoid scales.
Stomach J-shaped. Intestine with spiral valve.
(7) Respiration by 5 to 7 pairs of gills. Gill-slits separate and not covered
by Operculum. No air bladder and lungs.
(8) Heart 2–chambered (1 auricle and 1 ventricle). Sinus venosus and
conus arteriosus present. Both renal and portal systems present.
Temperature variable (poikilothermous).
(9) Kidneys opisthonephric. Excretion ureotelic. Cloaca present.
(10) Brain with large olfactory lobes and cerebellum. Cranial nerves 10
pairs.
(11) Olfactory sacs do not open into pharynx. Membranous labyrinth
with 3 semicircular canals. Lateral line canal system present.

c(12) Sexes separate. Gonads paired. Fertilization internal. Oviparous or

ovoviviparous.

Examples : True sharks- Dogfishes (Scoliodon), spiny dogfish (squalus)
seven gilled shark (Heptanchus), Zebra shark (stegostoma), hammer-
headed (Sphyrna), whale shark (Rhineodon).
Skates and rays-skate (Raja), stingray (Trygon), electric ray (Tropedo),
eagle ray (Myliobatis), guitar fish (Rhinobatus), sawfish (Pristis). Electric
organ are found in Torpedo
Rat fishes or chimaeras- Hydrolagus (= Chimaera).

Chapter 5 77

Scoliodon (Dog fish)
Scoliodon is carnivorous, feeding on other fishes, crabs, etc. It is
surface feeder. Both upper and lower jaws have homodont teeth. The
teeth are not meant for masticating the food, but for catching and
preventing the escape of the prey. Some pores called ampullary pores
are present on the upper and lower surface of the head; each pores
lead into an ampulla (plural. ampullae), called Ampulla of Lorenzini
through which the fish gets information about temperature variations
in the surrounding water. Behind the head on each side, are present
five oblique openings, known as gill slits, which communicate internally
with the pharynx. The gill slits expel the water out from the pharynx.
The caudal fins surrounds the tail, exhibiting asymmetry (upper
epicaudal lobe and lower hypo caudal lobe). Such a type of tail, in
which two different kinds of lobes are present, is known as
heterocercal tail. Numerous dermal placoid scales are embedded in
the skin for protection. The male has a pair of claspers attached to the
pelvic fins. The claspers help in the copulation. It is also eaten as food
and yields liver oil. Shark is viviparous. Mermaid purse is egg case of

cshark.
Torpedo (Electric Ray)

Torpedo is bottom dwelling, carnivorous fish which stuns or kills the
prey and enemies with electric shock from its electric organs. The
electric organs are modified muscles. Large openings called spiracles
are present behind the eyes and are used for talking water inside for
breathing.

Chapter 5 78

Osteichthyes (Bony fishes)
General Characters:
(1) Inhabit all sorts of water-fresh, brackish or salt.
(2) Body spindle-shaped and streamlined.
(3) Fins both median and paired, supported with fin rays of cartilage or
bone. Tail usually homocercal.
(4) Skin with dermal scales of 3 types; ganoid, cycloid or ctenoid. No
placoid scales.

c(5) Endoskeleton chiefly of bone (Gr., osteon, bone + ichthyes, fish).

Cartilagenous in sturgeons. Notochord replaced by distinct vertebrae
Claspers absent.
(6) Mouth terminal or sub terminal. Jaws usually with teeth.
Cloaca absent, anus present.
(7) Respiration by 4 pairs of gill covered by an operculum.
(8) An air (swim) bladder often present. Lung-like in some (Dipnoi.
(9) Ventral heart 2-chambered (1 auricle + 1 ventricle). Sinus venosus
and conus arteriosus present. Aortic arches 4 pairs. Erythrocytes oval,
nucleated. Temperature variable (poikilothermous).
(10) Adult kidneys mesonephric. Ammonotelic.

Chapter 5 79

(11) Brain with very small olfactory lobes, cranial nerves 10 pairs.
(12) Well developed lateral line system. Internal ear with 3 semicircular
canals.
(13) Sexes separate. Gonads paired. Fertilization usually external.
Mostly oviparous, rarely ovoviviparous or viviparous.

Classification of Osteichthyes
Subclass I. Sarcopterygii : (Gr., sarcos, fleshy + pterygium, fin)
(1) Paired fins leg-like or lobed.
(2) Olfactory sacs usually connected to mouth cavity by internal nostrils
or choanae, hence also called as choanichthyes (Gr., choana, funnel +
ichthyes, fish).
(3) Popularly called fleshy or lobe-finned, or air breathing fish.
Divided into 2 orders: Crossopterygii and Dipnoi.
Order 1. Crossopterygii – (Gr., crossoi, a fringe + pteryx, fin)
(1) Paired fins lobe like.
(2) Internal nares present or absent. Spiracles present.
(3) Air bladder vestigial.
Example– Primitive fleshy-finned extinct fishes.
Single living genus Latimeria.
Order 2. Dipnoi – (Gr., di, double + pnoe, breathing)

c(1) Internal nares present and spiracles absent.

(2) Air bladder single or paired, lung-like
Examples – Lung fishes. Only 3 living genera of lung fishes:
Neoceratodus(Australian lung fish), Protopterus(African lung fish) and
Lepidosiren(South American lung fish)

Subclass II. Actinopterygii – (Gr., actis, ray + pteryx, fin)
(1) Paired fins thin, broad, without fleshy lobes.
(2) Olfactory sacs not connected to mouth cavity.
(3) Popularly called ray-finned fishes.
They are divided into 3 orders: Chondrostei, Holostei and Teleostei.
Chondrostei – (Gr., chondros, cartilage + osteon, bone)

Chapter 5 80

(1) Primitive ray-finned cartilaginous ganoids.
Examples – Acepenser (Sturgeon), Polyodon (paddlefish)
Holostei – (Gr., holos, entire + osteon, bone)
(1) Ganoid or cycloid scales. Intermediate ray-finned fish, transitional
between Chondrostei and Teleostei Examples –Lepisosteus (garpike)
Teleostei – (Gr., teleos, complete + osteon, bone) (1) Scales cycloid,
ctenoid or absent.
(2) A hydrostatic swim bladder usually present.
(3) Advanced or modern ray-finned fishes
Examples – Harpodon (Bombay duck) Cyprinus (carp), Labeo rohita
(rohu), Catla, Carassius (Goldfish), Clarius (Magur), Heteropneustes
(singhi), Wallago (lachi), Mystus (tengra), Electrophorus (electric eel)
Anguilla (freshwater eel), Muraena (moray) Hemirhamphus (half beak),
Belone (garfish), Hippocampus (sea horse), Syngnathus (pipe fish),
Fistularia (flute fish) Ophiocephalus or channa (snake head),
Symbranchus (eels),Pterois (scorpion fish), Pleuronectes, Synaptura,

cSolea, Echeneis or Remora (sucker fish), Tetrodon (globe fish).

Chapter 5 81

Scales:

1. Cosmoid: These are not found in living fishes and are
composed of four distinct layers - outermost ganoine,
followed by cosmine, spongy bone and innermost compact
bone.

2. Placoid: They have a backwardly directed spine arising from
a basal plate.

3. Ganoid or rhomboid scales are thick, diamond or rhomboid
plates.

4. Cycloid: These are thin, flexible, circular in outline, marked
with concentric lines of growth which can be used for
determining age.

c5. Ctenoid: They have numerous small comb likes spines.

Chapter 5 82

Amphibia
General characters
(1) The amphibians can live only in fresh water and on moist land, and
are carnivorous, cold blooded, oviparous, tetrapod vertebrates.
(2) Head distinct, trunk elongated. Neck and tail may be present or
absent.
(3) Usually 2 pairs of pentadactyle limbs (tetrapod), some limb less.
Paired fins absent. Median fins, if present, without fin rays.
(4) Skin soft, moist and glandular. Pigment cells (chromatophores)
present.
(5) Exoskeleton absent. Digits claw less. Some with hidden dermal
scales.
(6) Endoskeleton mostly bony. Notochord replaced by vertebral
column. Skull dicondylic with 2 occipital condyles.
(7) Upper or both jaws with small homodont teeth. Tongue often
protrusible. Alimentary canal opens into cloaca.
(8) Respiration by lungs, skin and mouth lining. Larvae with external
gills which may persist in some aquatic adults.
(9) Heart 3–chambered (2 auricles + 1 ventricle). Sinus venosus present.
Aortic arches 1-3 pairs. Renal and hepatic portal systems well
developed Erythrocytes large, oval and nucleated. Body temperature

cvariable (poikilothermous).

(10) Kidneys mesonephric. Urinary bladder large. Excretion ureotelic.
(11) Brain poorly developed. Cranial nerves 10 pairs.
(12) Nostrils open into buccal cavity. Middle ear with a single rod-like
ear ossicle, called columella. Larval forms and some aquatic adults with
lateral line system.
(13) Sexes separate. Male without copulatory organ. Gonoducts open
into cloaca. Fertilization mostly external. Females mostly oviparous.
(14) Development indirect. Cleavage holoblastic but unequal. No extra–
embryonic membranes. Larva a tadpole which metamorphoses into
adult
Classification:

Chapter 5 83

The living amphibians have 2,500 species. They dominated the World
during carboniferous period.
Subclass I. Stegocephalia (Extinct) – Limbs pentadactyle. Skin with
scales and bony plates.
Order 1. Labyrinthodontia – Oldest known tetrapods called stem
Amphibia. Example – Eryops.
Order 2. Phyllospondyli – Small salamander-like. Example –
Branchiosaurs (Ichthyostega).
Order 3. Lepospondyli – Small salamander or eel-like. Examples –
Diplocaulus, Lysorophus.

Subclass II. Lissamphibia (living) –
Modern Amphibia without dermal bony skeleton.

Order 1. Gymnophiona or Apoda – (Gr., gymnos, naked + ophioneos,
serpet-like) or (Gr., a, without + podos, foot)
(1) Limb less, blind, elongated worm like, burrowing tropical forms
known as caecilians.
(2) Tail short or absent, cloaca terminal.
(3) In some dermal scales embedded in skin.
(4) Skull compact, roofed with bone.

c(5) Limb girdle absent.

(6) Males have protrusible copulatory organs,
Examples - Ichthyophis, Uroaeoryphlus.
Ichthyophis is a Limb less amphibian.

Order 2. Urodela or Caudata – (Gr., Ura, tail + delos, visible) or (L.,
cauda, tail)
(1) Lizard-like amphibians with a distinct tail and with 2 pairs of limbs.
(2) Skin devoid of scales.
(3) Gills permanent or lost in adult.
(4) Males without copulatory organs.
(5) Larvae aquatic, adult-like, with teeth.

Chapter 5 84

Examples – Ambystoma (Tiger salamander), Salamandra (salamander),
Amphiuma (congo eel), Plethodon. Siren (mud eel).

Order 3. Salientia or Anura – (L., saliens, leaping ) or (Gr., an, without +
nura, tail)
(1) Amphibia without tail in adults.
(2) Hind limbs usually adapted for leaping and swimming.
(3) Adults without gills or gill openings.
(4) Tympanum present.
(5) Skin loosely-fitting without scales.
(6)Fertilization always external.
Examples – Alytes (midwife toad), Pipa(Surinam toad), Xenopus(African
toad), Bufo (common toad), Hyla (tree toad), Gastrotheca (marsupial

cfrog), Rana (common frog), Polypedates or Rhacophorus (tree frog) .
Five representatives of classes of Amphibia: A.Salamander; B. Leopard
frog; C. Ichthyophis; D. A tropical tree toad; E. Mudpuppy

Practice Test Papers
1. In which of the following the notochord is present in embryonic stage

Chapter 5 85

(a) Vertebrates (b) Some chordates (c) All chordates (d) Non-chordates
2. In Urochordata notochord is found in
(a) Head of adult (b) Tail of adult (c) Tail of larva (d) Test of adult
3. The animal who possesses notochord throughout life is
(a) Fish (b) Amphioxus (c) Bird (d) Snake
4. Sea horse is an example of
(a) Mammalia (b) Pisces (c) Aves (d) Reptilia
5. Which of the following has a cartilagenous endoskeleton
(a) Elasmobranch (b) Dipnoi (c) Mollusca (d) Bony fishes
6. Torpedo is commonly known as

c(a) Sea horse (b) Electric ray (c) Globe fish (d) Sucker fish

7. Salamander belongs to the class
(a) Reptilia (b) Amphibia (c) Aves (d) Mammalia
8. Limbless amphibians belong to the order
(a) Anura (b) Urodela (c) Gymnophiana (d) Squamata
9. Midwife toad is another name for

Chapter 5 86

(a) Alytes (b) Hyla (c) Rhacophorus (d) Pipa

10.Tailless amphibians are the members of the group

(a) Salientia (Anura) (b) Gymnophiona (Apoda) (c) Urodela (Caudata) (d)
Cyclostomata

11. Elasmobranchs have …………scales.

12. Ctenoid scales are found in…….

13. Middle ear of amphibians has a single rod-like ear ossicle, called ……

14. Tetrapods includes three classes namely…..

15. The structure through which the fish gets information about
temperature variations in the surrounding water is known as …….

16. The male of chondrichthyes has a pair of claspers attached to the
pelvic fins. The claspers help in ……...

17. What does Agnatha refer to?

c18. Enlist scientific and common names of lung fishes.

Neoceratodus(Australian lung fish), Protopterus(African lung fish) and
Lepidosiren(South American lung fish)

19. Write down three most important characteristics of phylum
chordata:
(1) They have a notochord either throughout life or during early
embryonic development
(2) Dorsal hollow nerve chord
(3) Paired gill slits on either sides of pharynx at some stage; may or may
not be functional

Chapter 5 87

20. Give an outline classification of phylum chordata

Answers and Solutions

1.c

2. b

3. b

4. b c
5. a
6. b
7. b
8. a
9. a
10. a
11. Elasmobranchs have placoid scales.
12. Ctenoid scales are found in osteichthyes

13. Middle ear of amphibians has a single rod-like ear ossicle, called
collumella

14. Tetrapods includes three classes namely amphibians, reptiles,
mammals

15. The structure through which the fish gets information about
temperature variations in the surrounding water is known as Ampulla
of lorrenzini

Chapter 5 88

16. The male of chondrichthyes has a pair of claspers attached to the
pelvic fins. The claspers help in copulation

17. Agnatha refer to Jaw less primitive fish-like vertebrates without true
jaws and paired limbs

18. Enlist scientific and common names of lung fishes.
Neoceratodus(Australian lung fish), Protopterus(African lung fish) and
Lepidosiren(South American lung fish)

19. Write down three most important characteristics of phylum
chordata:
(1) They have a notochord either throughout life or during early
embryonic development
(2) Dorsal hollow nerve chord
(3) Paired gill slits on either sides of pharynx at some stage; may or may
not be functional

c20. Give an outline classification of phylum chordata

Chapter 5 89

Reptilia
General Characters :
Reptiles represent the first class of vertebrates fully adapted for life on
land.The characters of reptiles are a combination of the characters
found in fishes and amphibians on one hand and in birds and mammals
on the other. The class name refers to the mode of locomotion (L.,
repere or reptum, to creep or crawl), and the study of reptiles is called
Herpetology (Gr., herpeton, reptiles).
(1) Predominantly terrestrial, mostly carnivorous, air–breathing, cold–
blooded, oviparous and tetrapodal vertebrates.
(2) Body bilaterally symmetrical and divisible into 4 regions-head, neck,
trunk and tail.
(3) Two pairs of pentadactyle limbs, Digits provided with horny claws.
However, limbs absent in a few lizards and all snakes.
(4) Exoskeleton of horny epidermal scales, shields, plates and scutes.
(5) Skin dry, cornified and devoid of glands.
(6) Mouth terminal. Jaws bear simple conical teeth. In turtles teeth
replaced by horny breaks.
(7) Alimentary canal opens into a cloacal aperture.
(8) Endoskeleton bony. Skull with one occipital condyle
(monocondylic). A characteristic T–shaped inter clavicle present.

c(9) Heart usually 3–chambered, 4–chambered in crocodiles. Sinus

venosus reduced. 2 systemic arches present. Red blood corpuscles oval
and nucleated. Cold–blooded.
(10) Respiration by lungs throughout life.
(11) Kidney metanephric. Excretion uricotelic.
(12) Brain with more developed cerebrum than in Amphibia. Cranial
nerves 12 pairs.
(13) Lateral line system absent. Jacobson's organs present in the roof of
mouth used for smell.
(14) Sexes separate. Male usually with a muscular copulatory organ.
(15) Fertilization internal. Mostly oviparous. Large yolky meroblastic
eggs covered with leathery shells, always laid on land. Embryonic

Chapter 6 90

membranes (amnion, chorion, yolk sac and allantois) appear during
development. No metamorphosis. Young resemble adults.

Classification :
There are more than 7,000 living and several extinct species of reptiles,
grouped into 16 orders of which only 4 are living.
Subclass I Anapsida – Primitive reptiles with a solid skull roof. No
temporal openings.
Order 1. Chelonia or Testudinata : (Gr., chelone, turtle; L., testudo,
turtle)
(1) Body short, broad and oval.
(2) Limbs clawed and or webbed, paddle-like.
(3) Body encased in a firm shell of dorsal carapace and ventral plastron,
made by fusion of dermal bony plates. Thoracic vertebrae and ribs
usually fused to carapace.
(4) Skull anapsid, with a single nasal opening and without a parietal
Foramen. Quadrate is immovable.
(5) No sternum is found.
(6) Teeth absent. Jaws with horny sheaths.
(7) Cloacal aperture a longitudinal slit.
(8) Heart incompletely 4–chambered with a partly divided ventricle.

c(9) Copulatory organ single and simple.

(10) They include marine turtles, freshwater terrapins and terrestrial
tortoises.
Examples – Chelone, Testudo, Trionyx.

Subclass II Euryapsida (extinct) : Skull with a single dorso–lateral
temporal opening on either side bounded below by postorbital and
squamosal bones.

Subclass III Parapsida (extinct) : Skull with a single dorso–lateral
temporal opening on either side bounded below by the supra temporal
and post frontal bones.

Chapter 6 91

Subclass IV Synapsida (extinct) : Skull with a single lateral temporal
opening on either side bounded above by the postorbital and
squamosal bones.

Subclass V Diapsida : Skull with two temporal openings on either side
separated by the bar of postorbital and squamosal bones.

Order 2. Rhynchocephalia : (L., rhynchos, snout + Gr., kephale, head)
(1) Body small, elongated, lizard-like.
(2) Skull diapsid. Parietal foramen with vestigeal pineal eye present.
Quadrate is fixed.
(3) Numerous abdominal ribs present.
(4) Teeth acrodont.
(5) Heart incompletely four chambered.
(6) No copulatory organ in male.
Example: They are represented by a single living species, the “tuatara”
or sphenodon punctatum of New Zealand.

Order 3. Squamata : (L., squama, scale or squamatus, scaly)
(1) Skull diapsid. Quadrate movable.

c(2) Heart incompletely 4–chambered.

It includes snakes and lizards

Lacertilia - Lizards

Ophidia - Snakes

1. Saurology is the study of lizards.
2. Serpentology or ophiology is the study of snakes.
3. Lizards have 2 pairs of pentadactyl limbs with claw.
4. Autotomy is voluntary breaking of tail to confuse enemy. Tail of

most lizards is easily broken off when threatened or seized by a
predator. A new tail is soon regenerated but without vertebrae.

Chapter 6 92

5. Most lizards are oviperous, except two viviparous lizards-
Phrynosoma and Chameleon.

6. Draco- 'flying dragon', is a lizard which glides with the help of
patagium.

7. The only poisonous lizard in the world is Heloderma (Gila
monster), also called 'Beaded lizard' because its scales resemble
beads.

8. Heloderma rarely bites man, but is fatal. Its poison is neurotoxic.
9. Limbs are absent in lizards like ; Ophiosaurus, Anguis and

Rhineura, called as glass snakes.
10. Barkudia is a limbless lizard from South India.
11. The glass snakes Ophiosaurus derives its name from its

ability to break off its tail when seized.
12. A limbless lizard has movable eyelids and external ear

opening which are absent in snakes.
13. Lizards are mostly carnivarous, but a herbivorous lizard is

lguana from South and Central America.
14. The largest living lizard in the world is the ferocious dragon,

Varanus komodoensis, found in Malaya Archipelago.

Snakes

ci. Python and Boa have vestigial pelvic girdle and hindlimbs.

ii. Sternum, pectoral girdle, tympanum and urinary bladder are
absent in snakes.

iii. Eyelids of snakes are immovable, nictitating membrane is absent
and lungs assymetrical.

iv. The bifid tongue of snakes is sensitive to both odours and
vibrations.

v. A snake lacks middle ear.
vi. Moulting or ecdysis: Snakes shed off scaly epidermis of skin

periodically usually in one piece. This is termed moulting or

Chapter 6 93

ecdysis (moulting also occurs in arthropods). Snakes are not
found in New Zealand.
vii. Locomotion of snakes is carried out by ribs and large ventral
scutes.
viii. The largest nonpoisonous snake is Python.
ix. Eryx johnii or sand boa has a small, non-prehensile thick tail giving
a false resemblance to head, hence called 'double headed snake'.
Except Vipera russelli and Hydrophis, most of the snakes are
oviperous.
x. Cobras, kraits, vipers, sea snakes and coral snakes are common
poisonous snakes. All poisonous snakes possess poison gland
which are modified superior labial or parotid glands. The poison i
fangs (teeth) are maxillary teeth present on maxilla. Snake poison
is a mixture of enzymes and specific toxins and is a good digestive
juice. It is fatal only when mixed in blood. The snake venoms are
two types- neurotoxic and haemotoxic. The poisons of cobra,
krait and sea snakes are neurotoxins. Neurotoxins cause death by
paralysis of respiratory muscles and asphyxiation. Haemotoxins
are typical of vipers. Haemotoxins cause tissue destruction and
widespread hemorrhage. Proteolysin is present in the venom of
viper. The venom of viper affects circulatory system. The best

cmedicine to treat snake bite is a antivenin or antivenom serum

which contain antibodies. Different antivenins are required
against different snakes due to differences in the qualities of
snake venoms. Benadryl and antisera are used to couteract-the
effect of haemotoxins. An antivenin is prepared by injecting a
horse with increasing doses of a snake venom until the horse
becomes completely immunized . Blood serum of horse is
collected and preserved. In India, antivenin injections are
prepared at Haffkin's institute, Mumbai and Central Rsearch
Institute, Kausauli (Simla). Sea snakes are poisonous; Two
common sea snakes are Hydrophis and Enhydrina.

Chapter 6 94

Identification of poisonous and non poisonous snakes:-
The arrangement and size of scales, plates and shields help in
identification of poisonous and non-poisonous snakes. The common
characteristics of both the types are:

1. See the scale pattern on the ventral side(underside) of the snake.
If the scales are small and uniform, or are transversely long but
some rows of small scales of the back are visible on the underside,
it is non-poisonous.

2. If the scale pattern on the ventral side shows transversely
arranged plates and no small scales of the back reach the
underside, then it may be poisonous or non-poisonous. To
confirm, watch the scale pattern on the top of the head; if it is
covered with small scales, it is one of the deadly poisonous snakes
such as a viper.

3. But if the scales on the head are large shields or plates, it may be
non-poisonous or one of these poisonous snakes: a pit-viper, a
cobra, king cobra, a coral snake. To confirm, look at the side of the
face.

i. If a pit larger than the nostril is present between the nostril
and the eye, it is a pit-viper.

cii. If no pit is present but the third upper labial (supra labial)
scale touches the nasal scale and the eye, it is a cobra, king
cobra or a coral snake, Naja naja (cobra).
iii. If none of the two above characters is present, then look for

the following two characters:
a. the middle row of scales on the back enlarged and
b. the fourth scale on the lower lip (infra labial) along the
margin of the lower jaw is the largest, then it is a krait.

iv. If (i), (ii) and (iii) characters are absent, then its non-
poisonous.

Chapter 6 95

c4. All sea snakes are poisonous except one species. They have large
flattened scales on the head and the tails are flattened laterally.

Order 4. Crocodilia : (G., krokodeilos, Crocodile)
(1) Skin thick having scales, bony plates and scutes.
(2) Skull diapsid. Quadrate immovable. No parietal foramen.
(3) Abdominal ribs present.
(4) Heart completely four chambered.
Examples – Crocodylus, Gavialis, Alligator

Aves
General Characters:-

Chapter 6 96

(1) The birds are feather covered, air-breathing, warm-blooded,
oviparous, bipedal flying vertebrates.
(2)They have two pairs of limbs. Forelimbs are modified as wings for
flying. Hind limbs or legs are large, and are variously adapted for
walking, running scratching, perching, food capturing, swimming etc.
(3) Exoskeleton epidermal and horny.
(4) Skin dry without glands except the oil or preen gland/ uropygeal
gland at the base of tail.
(s5) Pectoral muscles of flight are well developed.
(6) Skull smooth and monocondylic, having a single occipital condyle.
Sutures indistinct.
(7) Vertebral column short. Vertebrae heterocoelous (saddle-shaped).
(8) Sternum large, usually with a vertical, mid ventral keel for
attachment of large flight muscles.
(9) Ribs double-headed (bicephalous) with posteriorly directed uncinate
processes.
(10) Both the clavicles and a single inter clavicle fuse to form a V–
shaped bone, called furcula or wishbone.
(11) Heart completely four chambered. No sinus venosus or truncus
arteriosus. Only right aortic (systemic) arch persists in the adult. Renal
portal system vestigial. Blood corpuscles nucleated.

c(12) Birds are the first warm blooded vertebrates. Body temperature is

constant (homoiothermous).
(13) Respiration by compact, spongy, distensible lungs continuous with
air-sacs.
(14) Larynx without vocal cords. A sound box or syrinx for producing
voice lies at or near the junction of trachea and bronchi.
(15) Kidneys metanephric. Uterus open into cloaca. Urinary bladder
absent. Birds are urecotelic. Excretory matter of urates is eliminated
with faeces.
(16) Sexes separate. Sexual dimorphism well marked.
(17) Fertilization internal, preceded by copulation and courtship.
Females oviparous.

Chapter 6 97

(18) Eggs develop by external incubation. Cleavage discoidal,
meroblastic. Development direct, Extra-embryonic membranes
(amnion, chorion, allantois and yolk-sac) present.
(19) Parental care well marked.

Classification:
About 9,000 living species of birds are known. 25 avian orders are
recognized. Class Aves is first divided into two subclasses.
Sub-Class I. Archaeornithes : Gr., archios, ancient + ornithos, bird)
(1) Extinct, Jurassic birds of Mesozoic Age, about 155 million years ago.
(2) Wings primitive, with little power of flight.
(3)Sternum without a keel.
(5) In Archacopteryx beak in toothed. This sub-classes includes a single
order
Order Archaeopterygiformes : Example – Archaeopteryx lithographica,
from Jurassic or Bavaria, Germany; one specimen lying in the British
museum, London, the other lying in the Berlin.

Sub-class II. Neornithes : (Gr., neos, modern+ ornithos, Birds)
(1) Modern as well as extinct post-Jurassic birds.
(2) Wings usually well-developed and adapted for flight, with few

cexceptions.

(3) Teeth absent except in some fossil birds.
(5) Sternum usually with a keel.
(6) Abdominal ribs absent
This sub-class is divisible into 4 super-orders:

Super-order 1. Odontognathae : (Gr., odontos, teeth)
(1) Extinct, Upper Cretaceous birds.
(2) Jaws with teeth.
Order 1. Hesperornithiformes Example – Hesperornis.
Order 2. Ichthyornithiformes Examples – Ichthyornis.

Chapter 6 98